14-37-00053, and by the A-TWAIN project, funded by the Arctic
Ocean program at the FRAM-High North Research Centre for
Climate and the Environment. We thank Henriksen Shipping
Service AS, for help with logistics. The mooring recovery and
deployment was a great team effort by all onboard the research
vessels Akademik Fedorov (2013) and Akademik Tryoshnikov

(2015). We thank our colleagues from the Arctic and Antarctic
Research Institute, Russia, particularly V. Vizitov, V. Zaitsev, and
E. Morozova, for their help with cruise preparations. All mooring data
used in this study are available on the web at https://arcticdata.
io/catalog/#view/arctic-data.7792.4. All authors participated in
data processing and preliminary analysis; A.V.P., I.M.A., I.V.P., R.R.,
and V.V.I. carried out statistical analysis of data; R.Kw. provided
sea-ice information and processing; T.K. processed Fram Strait
data; A.S. provided processing and analysis for Svalbard mooring
data; A. Y. analyzed fast-ice thickness data; and T.M.B. worked with
reanalysis data. All authors contributed to interpreting the data
and writing the paper. The authors declare no competing financial
interests.

We report the discovery of a multiply imaged, gravitationally lensed type Ia supernova,
iPTF16geu (SN 2016geu), at redshift z = 0.409. This phenomenon was identified because
the light from the stellar explosion was magnified more than 50 times by the curvature of
space around matter in an intervening galaxy. We used high-spatial-resolution observations
to resolve four images of the lensed supernova, approximately 0.3 arc seconds from the
center of the foreground galaxy. The observations probe a physical scale of ~1 kiloparsec,
smaller than is typical in other studies of extragalactic gravitational lensing. The large
magnification and symmetric image configuration imply close alignment between the lines
of sight to the supernova and to the lens. The relative magnifications of the four images
provide evidence for substructures in the lensing galaxy.

One of the foundations of Einstein’s theory of General Relativity is that matter curves the surrounding space-time. For the rare cases of nearly perfect alignment of an astronomical source, an intervening massive object, and the observer, multiple images of
a single source can be detected—a phenomenon
known as strong gravitational lensing.

PS1-10afx, a lensed SN Ia at redshift z = 1.388
with a large amplification (m 30) where multiple
images could have been expected, was reported
several years ago (6 ). A foreground lens was later
identified at z = 1.117 (7). At the time of the discovery, several interpretations were discussed, including a superluminous supernova (8). Because
the lensed SN Ia hypothesis did not gain acceptance until long after the explosion had faded, no
high-spatial-resolution imaging could be carried
out in that case to verify the strong lensing nature of the system. Multiple images of another
supernova, SN Refsdal (9), were discovered in a
Hubble Space Telescope (HST) survey of the
massive galaxy cluster MACS J1149.6+2223. As the
source was identified as a core-collapse supernova, it could not be used to measure the lensing
magnification directly.

Thanks to the well-known characteristics of
their time-dependent brightness in optical and
near-infrared (NIR) filters (the SN light curves),